Vibration control is a common engineering problem. In some applications such as shaking, mixing, polishing, sifting, sanding and others too numerous to list, vibration is desirable and employed productively. In other applications vibration is not desired but is present through the dictates of physical laws governing the acceleration of mass produced by oscillatory forces. These involve the function and use of such items as motors, pumps, gear boxes, rotors, automatic weapons and other devices too numerous to list. In many of the above applications it is desirable to reduce or eliminate the oscillatory forces that produce vibration in other attached bodies or supporting structure. The attached body or supporting structure is generally referred to as the isolated body.
Various vibration control devices have been developed heretofore for the purpose of reducing the oscillatory force transfer between a vibrating body and a body for which vibration is unwanted. These vibration control devices are referred to as vibration isolators. Vibration isolators are broadly categorized as being an active vibration isolator or a passive vibration isolator. Devices of the two categories generally function to control the oscillatory force transfer between a vibrating body and an isolated body. One of the laws of Newtonian physics states that all unbalanced forces act to accelerate masses. This law is summed up in the familiar equation, F=ma, where: F=the unbalanced force, m=the mass of the object the force acts on, a=the acceleration of the mass produced by the force. From this law it can be shown that the only methods by which vibration can be reduced is by producing a balancing force or by absorbing the force through acceleration of other masses.
By way of explanation, an active vibration isolator draws its energy and/or actuation from an independent and separate source of power that is not germane to the source of energy causing the oscillatory force which is to be controlled or cancelled. The active vibration isolator converts the energy from the external power source into forces which oppose or serve to cancel the oscillatory force transfer from the vibrating body to the isolated body. Additional controls, power and peripheral devices are required to operate an active vibration isolator at the proper amplitude, frequency and phase. Additional space is required for the necessary controls, the power source, the required peripheral equipment and the moving components of the active vibration control device itself. Although they function well, active vibration control devices are thus relatively complex and expensive, and are not weight or space efficient.
On the other hand, the design of a passive vibration control device avoids these undesirable and unwanted features. It is generally less complex in physical design, function and performance, but it is harder for it to maintain the proper amplitude frequency and phase. There are three basic types of passive isolators. They are: spring isolators, damping isolators, and mass isolators. Spring isolators reduce the oscillatory forces transmitted to the isolated body by introducing resilience between the vibrating body and the isolated body. Only at a vibration frequency that is high relative to the natural frequency of the system will a spring isolator perform well. This is because a spring transmits a force to the isolated body that is equal to the product of the spring rate of the spring times the relative motion between the two bodies. Since at high frequency this relative motion is small, the force transmitted is also small. The resilience allows the vibrating body to vibrate more thus its own mass absorbs the extra force. Damping isolators reduce the oscillatory forces by producing frictional or viscous forces (called damping) that are proportional to the relative velocity between the vibrating body and the isolated body. At low frequencies these damping forces are small because the relative velocity between the two bodies is small. Again the extra force is absorbed by greater acceleration of the vibrating body, but a damper has no static strength. Mass isolators reduce the oscillatory forces transmitted to the isolated body by simply introducing additional mass into the system; thus, the isolated body's acceleration is decreased. In addition to the three basic types of isolators, there are very many isolators that incorporate two or more of the basic types into one system. These include spring-dampers like the automotive suspension, mass-dampers like the fluid coupled flywheel, and spring-mass isolators like the frahum absorber, centrifugal, pendulum, and the Bifilar.
More recently, a spring-mass passive vibration isolator has been developed which employs inertial amplification and cancellation principles. These isolators use a principle of harmonic motion that the acceleration of a body is exactly out-of-phase with its displacement. Because of this law of physics an oscillatory force produced by a spring attached to the isolated body can be completely or partially cancelled by the forces produced by the acceleration of a third body's mass if its motion can be forced to be proportional to the displacement between the vibrating body and the isolated body. This forced motion has been accomplished successfully by various combinations of beams, levers and bearings to amplify the motion of the third mass (called the tuning mass) to large accelerations so that the force produced by its inertia is high enough to cancel the force produced by the spring. For example, vibration isolation through nodalization involves locating the isolated body attachment points along a flexible beam (the spring) coinciding with the locations of nodal or vibrational null points created by tuning masses on the ends of the beam. However, these systems, like the nodal beam, DAVI, and IRIS, are complex and require extra space for the large motions of the beams, levers and tuning mass.
Thus, there is a need for an improved vibration control device which employs inertia cancellation principles and which will function over a wide range of physical and vibratory environment. The improved vibration control device should be of reduced weight, size and complexity and should not be burdened by the limitations and disadvantages of existing vibration control devices.